Bed pads and seat pads are sometimes employed in medical settings to prevent bed sores or used to reduce fatigue and provide comfort in situations where prolonged sitting or resting in one place is required. These devices function by repeatedly and alternately inflating and deflating adjacent air channels in the pad or cushion so that the supporting pressure on any one part of the human body is in constant change.
In such known pad systems, the directing of the required air pressure is accomplished by use of a timer operated by alternating current (e.g., 60 hz) and a valve which is electrically operated as directed by the timer. This dependence on alternating current is costly and a great disadvantage particularly in an application (such as a wheelchair or automobile) where alternating current is not available.